PROJECT SUMMARY ? Project 3 Addiction to drugs of abuse produces pathological changes in synaptic physiology that impair the capacity of the prefrontal cortex (PFC) to communicate with the nucleus accumbens, and impede the successful regulation of drug seeking. The Center for Opioid and Cocaine Addiction (COCA) studies the genetic, cellular and physiological mechanisms of relapse in the PFC and nucleus accumbens rodent models and bidirectionally translates this with COCA clinical studies using fMRI read-out of treatments with N-acetylcysteine (NAC) and PFC transmagnetic stimulation (TMS) for cue reactivity in cocaine users. Project 3 specifically explores the nucleus accumbens for synaptic adaptations after heroin and cocaine self-administration in mice and rats, and the adaptations that occur during cue-induced drug seeking. We find both enduring changes in withdrawal and transient changes during cue-induced heroin and cocaine seeking that are correlated with the intensity of the relapse event. These changes are present in all four compartments of the synapse (pre- and postsynapse, astroglia and extracellular matrix). By simultaneously examining the 4 synaptic compartments of the tetrapartite synapse, we are accessing processes heretofore poorly studied in relation to addiction, which may contain unique opportunities for therapeutic development. Animal & Validation Core B will provide rats and mice trained to self- administer heroin or cocaine. Our endpoints include cell morphology, cell signaling and physiological processes. Specifically, we will measure enduring and cue-induced transient changes in the morphology, synaptic glutamate-mediated currents and protein expression in specific cell types in the accumbens using transgenic rats and mice and cell-specific viral mediated expression of transgenes in the nucleus accumbens. Finally, pursuant to an overarching COCA goal to understand which cell type and neuronal subpopulation is mediating the effects of cue-induced heroin and cocaine seeking, we administer the treatments used in the clinical Project 4 (NAC and continuous theta burst stimulation) to provide bidirectional construct validity for the relapse-related discoveries in Project 3.